The field of the invention pertains to methods of manufacturing semiconductor devices, such as solar cells, and in particular, to methods of manufacturing wafers of semiconductor material used in manufacturing semiconductor devices.
Much of the relatively high cost of many forms of semiconductor devices is due to the cost of crystalline semiconductor material and the waste of such material in producing semiconductor devices from ingots of the material. Therefore, substantial attention has been given to improving the efficiency of methods of producing semiconductor wafers used in making semiconductor devices. Somewhat related to this, solar cells, one of the common forms of semiconductor devices, having straight sides (e.g., a generally square-shaped configuration) have been found to be desirable for efficient arrangements of solar cells in solar panels.
One conventional approach to providing wafers for such solar cells involves grinding an ingot into a round shape and then sawing pairs of opposed elongated planes along the ingot. The ingot, as grown, of course has a curved surface along its direction of elongation. However, the surface is somewhat irregular. After cropping the ends of the ingot to provide generally flat end surfaces, the ingot is clamped for the above grinding. Attempting to position the ingot in the clamps to reduce wastage in grinding from the irregular to the round shape is typically a far from ideal process. Specifically, typically, feelers along the apparatus help the operator approximately determine the optimal position for the ingot in the clamps to minimize the amount of material ground off in provding the round shape.
In the slabbing process (to provide the opposed elongated planes), similar inaccuracies, resulting in wastage of valuable material, generally prevail. For example, typically, the rounded ingot is centered before clamping along stops under the ingot and also along one side of the ingot. Then the ingot is sawed along its direction of elongation to provide a pair of opposed planes. These planes, in the ideal, would be perfectly parallel. However, due to equipment limitations (e.g., the tendency of the saws to angle outwardly as they move through the ingot), the ideal of course is never attained. After the first pair of opposed planes is provided, one would be typically used in re-positioning the ingot for sawing to provide the second pair of opposed planes. The inaccuracies in that reference plane, coupled with the above-indicated inaccuracies in the sawing itself, serve to compound the error in respect to the sawing to provide the second pair of opposed planes.
U.S. Pat. No. 4,487,989, having the same assignee as the present matter, reveals some helpful variations in, for example, the process just described. Specifically, it reveals the advantages which can be garnered from slabbing the ingot to provide the pairs of opposed planes first and, then, grinding the corner regions to round them off, to flatten them, or, alternatively, eliminating that grinding altogether and leaving the corner regions irregular. However, the difficulty and wastage resulting from the inaccuracies in positioning the ingot for slabbing and grinding, remained unaddressed.
The present invention significantly addresses this area of concern. In the course of doing so, it incorporates the mounting of ingot mounting structures on the cropped ends of an ingot. These structures have particular shapes in connection with particularly shaped fixture structures in which the mounting structures are positioned during processing of the ingot. For accuracy of placement of the mounting structures on the cropped ingot ends, crystallographic node lines are employed for reference purposes. The method incorporates ease of performance, significant savings in material, and the capability for readily meeting desired tolerances for semiconductor wafers.